1. Field of the Invention
The present invention relates to an improvement in a biological method of treating wastewater. More particularly, the present invention relates to a biological method of removing dissolved organic substances, and nitrous and phosphorus materials present in wastewater efficiently in a batch reactor containing porous biomass carriers.
2. Description of the Prior Art
In general, wastewater includes organic substances, nitrous and phosphorus materials, and the like, which serves as a nutrient source necessary for certain microorganisms to carry out their metabolism. The methods utilizing this type of biological function of the microorganisms in the field of wastewater treatment are called "biological methods for treatment of wastewater."
Conventionally, the methods involving the treatment of wastewater comprises transferring pollutants such as organic substances, and nitrous and phosphorous materials into microcells or converting these pollutants into environmentally innoxious form through a biological reaction, and separating the resultant microbes and innoxious product from the wastewater for disposal.
A wide variety of microorganisms and environmental conditions can be utilized depending on the type of the pollutant to be treated. For example, organic substances are converted into carbon dioxide and water by the action of heterotrophic microorganisms intaking such organic substances as a carbon source under aerobic conditions, and into methane, carbon dioxide, hydrogen, water, etc., under anaerobic conditions. Nitrogen is converted into oxidative nitrogen such as nitrite or nitrate by nitrifying bacteria under aerobic conditions. However, under anoxic conditions (i.e., under dissolved oxygen free conditions), nitrogen is converted into an innoxious form such as nitrogen or nitric acid gas through a denitrification reaction by the action of heterotrophic microorganisms. Phosphorus is uptaken in the form of a dissolved phosphorus by a bacteria having phosphorus accumulating capacity, and accumulated therein in the form of granules under an aerobic conditions. However, the phosphorus granule thus accumulated are released from the microorganisms in the form of a dissolved phosphorous under anaerobic condition (i.e., under dissolved oxygen and nitric acid free conditions).
In order to maximize the efficiency of the biological treatment of wastewater, it is necessary to choose proper microbes depending on the type of pollutant to be treated and provide suitable environmental conditions for growth to enhance the microbial activity, as well as increasement in the amount of microorganisms within the reactor.
Several methods have been hitherto proposed in attempt to enhance the activity of microorganisms used. According to one of these methods, the reactor is partitioned spatially so as to provide efficient conditions for the growth of the microorganisms. However, this method has drawbacks that it requires broad spaces of the treatment facilities and, therefore, enormous capital investment for constructing the treatment facilities. Furthermore, the method suffers from the defects that the manipulation of treatment facilities is grossly complicated.
As an improvement of this method, it has been proposed to increase the concentration of microorganisms by recycling the produced microorganisms or adding a biomass carrier to the partitioned reactor. This improved method could reduce the required treatment facilities spaces to some extent. However, it still requires broad spaces for treatment facilities, resulting in higher capital investment.
Another approach was a slurry type treatment method using a batch reactor, in which the reaction conditions are changed with the lapse of time by controlling the amount of dissolved oxygen. However, this method could not increase the concentration of microorganisms to above 5,000 mg/L because the sedimentation for separating the resultant sludge from the treated wastewater must also be carried out in the same reactor. Thus, this method is not suitable for treating a large volume of wastewater.
In addition, separation of the surplus sludge from the treated wastewater has been carried out mainly by a gravitational sedimentation method or a floatation method. However, the resultant sludge has a low concentration and, thus, this type of separation method must be accompanied by expensive, additional treatment procedures in order to attain the resultant sludge in a high concentration.